1. Field of the Invention
The present invention relates to xyloglucanases belonging to family 44 of glycosyl hydrolases, preferably to enzymes exhibiting xyloglucanase activity as their major enzymatic activity in the neutral and alkaline pH ranges; to a method of producing such enzymes; and to methods for using such enzymes in the textile, detergent and cellulose fiber processing industries.
2. Description of Related Art
Xyloglucan is a major structural polysaccharide in the primary (growing) cell wall of plants. Structurally, xyloglucans consists of a cellulose-like beta-1,4-linked glucose backbone which is frequently substituted with various side chains. The xyloglucans of most dicotyledonous plants, some monocotyledons and gymnosperms are highly branched polysaccharides in which approx. 75% of the glucose residues in the backbone bear a glycosyl side chain at O-6. The glycosyl residue that is directly attached to the branched glucose residue is invariably alfa-D-xylose. Up to 50% of the side chains in the xyloglucans contain more than one residue due to the presence of beta-D-galactose or alfa-L-fucose-(1-2)-beta-D-galactose moieties at O-2 of the xylose residues (C. Ohsumi and T. Hayashi (1994) Plant and Cell Physiology 35:963-967; G. J. McDougall and S. C. Fry (1994) Journal of Plant Physiology 143:591-595; J. L. Acebes et al. (1993) Phytochemistry 33:1343-1345). On acid hydrolysis, the xyloglucan extracted from cotton fibers yielded glucose, xylose, galactose and fucose in the ratio of 50:29:12:7 (Hayashi et al., 1988).
Xyloglucans produced by solanaceous plants are unusual in that typical only 40% of the beta-1,4-linked glucose residues bear a glycosyl side chain at O-6. Furthermore, up to 60% of the xylose residues are substituted at O-2 with alfa-L-arabinose residues and some solanaceous plants, such as potato, also have xyloglucans with beta-D-galactose substituents at O-2 of some of the xylose residues (York et al (1996)).
Xyloglucan is believed to function in the primary wall of plants by cross linking cellulose-micro fibrils, forming a cellulose-xyloglucan network. This network is considered necessary for the structural integrity of primary cell walls (Carpita et al., 1993). Another important function of xyloglucan is to act as a repository for xyloglucan subunit oligo saccharides that are physiologically active regulators of plant cell growth. Xyloglucan subunits may also modulate the action of a xyloglucan endotransglycosylase (XET), a cell wall associated enzyme that has been hypothesized to play a role in the elongation of plant cell walls. Therefore xyloglucan might play an important role in wall loosening and consequently cell expansion (Fry et al., 1992).
The seeds of many dicotyledonous species contain xyloglucan as the major polysaccharide storage reserve. This type of xyloglucan, which is localized in massive thickenings on the inside of the seed cotyledon cell wall, is composed mainly of glucose, xylose and galactose (Rose et al., 1996).
Seeds of the tamarind tree Tamarindus indica became a commercial source of gum in 1943 when the gum was found useful as a paper and textile size. Sizing of jute and cotton with tamarind xyloglucan has been extensively practiced in Asia owing to the low cost of the gum and to its excellent properties. Food applications of tamarind xyloglucan include use in confections, jams and jellies and as a stabilizer in ice cream and mayonnaise (Whistler et al., 1993).
Xyloglucanase activity is not included in the classification of enzymes provided by the Enzyme Nomenclature (1992). Hitherto, this enzymatic activity has simply been classified as glucanase activity and has often been believed to be identical to cellulolytic activity (EC 3.2.1.4), i.e. activity against xcex2-1,4-glycosidic linkages in cellulose or cellulose derivative substrates, or at least to be a side activity in enzymes having cellulolytic activity. However, a true xyloglucanase is a true xyloglucan specific enzyme capable of catalyzing the solubilisation of xyloglucan to xyloglucan oligosaccharides but which does not exhibit substantial cellulolytic activity, e.g. activity against the conventionally used cellulose-like substrates CMC (carboxymethylcellulose), HE cellulose and Avicel (microcrystalline cellulose). A xyloglucanase cleaves the beta-1,4-glycosidic linkages in the backbone of xyloglucan.
Xyloglucanase activity is disclosed in Vincken et al. (1997) wherein three different endoglucanases EndoI, EndoV and EndoVI from Trichoderma viride (similar to T. reesei) are characterized. EndoI, EndoV and EndoVI belongs to family 5, 7 and 12 of glycosyl hydrolases, respectively, see Henrissat, B. et al. (1991, 1993).
International Patent Publication WO 94/14953 discloses a family 12 xyloglucanase (EG II) cloned from the fungus Aspergillus aculeatus and expressed in the fungus Aspergillus oryzae. 
International Patent Publication WO 99/02663 discloses xyloglucanases cloned from Bacillus licheniformis (family 12) and Bacillus agaradhaerens (family 5) and expressed in Bacillus subtilis. 
It is an object of the present invention to provide an enzyme with a high xyloglucanase activity at an alkaline pH which xyloglucanase exhibits excellent performance in conventional detergent compositions.
The inventors have now found enzymes having substantial xyloglucanase activity, which enzymes belong to family 44 of glycosyl hydrolases and perform excellent in conventional detergent compositions, especially in liquid detergent compositions.
Accordingly, the present invention relates to an enzyme preparation comprising a xyloglucanase belonging to family 44 of glycosyl hydrolases and exhibiting a relative activity of at least 30% between pH 5.0 and 8.0.
The inventors have also succeeded in cloning and expressing a family 44 xyloglucanase. Accordingly, in further aspects the invention relates to a family 44 xyloglucanase which is (a) a polypeptide encoded by the DNA sequence of positions 121-1677 of SEQ ID NO:1, (b) a polypeptide produced by culturing a cell comprising the sequence of SEQ ID NO:1 under conditions wherein the DNA sequence is expressed, (c) a xyloglucanase enzyme having a sequence of at least 60% identity to positions 40-559 of SEQ ID NO:2 when identity is determined by GAP provided in the GCG program package using a GAP creation penalty of 3.0 and GAP extension penalty of 0.1, or (d) a polypeptide encoded by a DNA sequence that hybridizes to the DNA sequence of SEQ ID NO: 1 under medium stringency conditions, wherein the medium stringency conditions comprise hybridization in 5xc3x97SSC at 45xc2x0 C. and washing in 2xc3x97SSC at 60xc2x0 C.; or (e) a polypeptide encoded by the xyloglucanase encoding part of the DNA sequence obtainable from the plasmid in Escherichia coli DSM 13321; and to a family 44 xyloglucanase which is (a) a polypeptide encoded by the DNA sequence of positions 121-1677 of SEQ ID NO:3, (b) a polypeptide produced by culturing a cell comprising the sequence of SEQ ID NO:3 under conditions wherein the DNA sequence is expressed, or (c) a polypeptide encoded by the xyloglucanase encoding part of the DNA sequence obtainable from the plasmid in Escherichia coli DSM 13322; and to a family 44 xyloglucanase which is (a) a polypeptide encoded by the DNA sequence of positions 121-1677 of SEQ ID NO:5, (b) a polypeptide produced by culturing a cell comprising the sequence of SEQ ID NO:5 under conditions wherein the DNA sequence is expressed, or (c) a polypeptide encoded by the xyloglucanase encoding part of the DNA sequence obtainable from the plasmid in Escherichia coli DSM 13323; and to an isolated polynucleotide molecule encoding a polypeptide having xyloglucanase activity which polynucleotide molecule hybridizes to a denatured double-stranded DNA probe under medium stringency conditions, wherein the probe is selected from the group consisting of DNA probes comprising the sequence shown in positions 121-1677 of SEQ ID NO:1, 3 or 5, and DNA probes comprising a subsequence of positions 121-1677 of SEQ ID NO:1, 3 or 5, the subsequence having a length of at least about 100 base pairs.
In further aspects, the invention provides an expression vector comprising a DNA segment which is e.g. a polynucleotide molecule of the invention; a cell comprising the DNA segment or the expression vector; and a method of producing a exhibiting xyloglucanase enzyme, which method comprises culturing the cell under conditions permitting the production of the enzyme, and recovering the enzyme from the culture.
In yet another aspect the invention provides an isolated xyloglucanase enzyme characterized in (i) being free from homologous impurities and (ii) being produced by the method described above.
The novel enzyme of the present invention is useful for the treatment of cellulosic material, especially cellulose-containing fiber, yarn, woven or non-woven fabric. The treatment can be carried out during the processing of cellulosic material into a material ready for garment manufacture or fabric manufacture, e.g. in the desizing or scouring step; or during industrial or household laundering of such fabric or garment.
Accordingly, in further aspects the present invention relates to a detergent composition comprising a xyloglucanase enzyme having substantial xyloglucanase activity in the neutral or alkaline range; and to use of the enzyme of the invention for the treatment of cellulose-containing fibers, yarn, woven or non-woven fabric.
The present invention has now made it possible to use a xyloglucanase in detergent compositions for removing or bleaching certain soils or stains present on laundry, especially soils and spots resulting from xyloglucan-containing food, plants, and the like. Further, it is contemplated that treatment with detergent compositions comprising the novel enzyme can prevent binding of certain soils to the xyloglucan left on the cellulosic material.